The present invention relates generally to a vehicle four-wheel-drive transfer case, and in particular to a four-wheel-drive transfer case which provides automatic torque balancing, differentiation, and traction enhancement in the event of wheel slip.
Four-wheel-drive systems for vehicles are being utilized to a greater extent, providing increased traction and safety of operation for the vehicle. Recently, "full time" four-wheel-drive systems have been developed for vehicles, wherein a transfer case is typically provided with an interaxle differential for dividing torque between the vehicle front and rear differentials. The torque transfer mechanisms to supply drive power to the four wheels of a vehicle are usually connected to the vehicle transmission which is driven by the vehicle engine.
In a vehicle provided with a "full time" two-wheel-drive system, to prevent excess slippage between the front and rear wheels, the transfer case has included a selectively engageable clutch, which is operative to lock the interaxle differential upon sensing predetermined slippage between the front and rear output shafts of the transfer case. As an example, a transfer case has been designed to utilize electronic control, and includes a planetary interaxle differential for proportional torque split. An electromagnetic clutch is locks the differential to enhance mobility when road coefficients cause single wheel or single axle traction loss. The actuation of the clutch system is monitored by an electronic module and sensor system, which can detect abnormal amounts of differentiation in the interaxle unit and correct for this differentiation. This type of system does improve vehicle handling and stability, but may not adequately balance torque between the front and rear axles, nor adequately account for differentiation in the full time four-wheel-drive system.
There has thus been found a need to provide improved torque balancing and differentiation along with the ability to provide extra torque in the event of single-wheel or single-axle traction loss for improved mobility and stability in a full time four-wheel-drive system associated with a vehicle.